The present invention relates to a voltage-boosting circuit suitable for use in an electronic device which is tested under conditions outside normal operating limits.
Many electronic devices have circuits which must operate at a boosted voltage level, exceeding the voltage supplied to other circuits in the device. In a dynamic random-access memory (DRAM), for example, the word-line driving circuits may require a boosted voltage. Voltage-boosting circuits such as charge pumps are widely employed to produce such boosted voltages.
Before shipment, electronic devices are often put through burn-in tests, in which the devices are intentionally stressed by continuous operation at an abnormally high voltage level, in a high-temperature environment. DRAMs, for example, are burned in so that memory cells prone to early failure can be discovered.
The boosted voltage generated by a conventional voltage-boosting circuit during a burn-in test is higher than the boosted voltage generated during normal operation, because the original power-supply voltage is higher. Since a burn-in test may last for a considerable time, circuit elements that receive the boosted voltage are sometimes damaged, even though these elements would not fail under normal operating conditions. The burn-in test then has the undesired result of reducing production yields by unnecessarily creating defective devices.